The horned sea snake gets its common name from the raised, horn-like spines above its eyes.

The horned sea snake is fully aquatic and has a flattened, paddle-like tail to help it swim.

The nostrils of the horned sea snake have valves that allow them to be closed to prevent water entering the lungs.

The horned sea snake has one of the most toxic venoms of all sea snakes, but no bites to humans have been documented.

The horned sea snake is classified as Least Concern (LC) on the IUCN Red List (1).

A fully aquatic and highly venomous snake, the horned sea snake (Acalyptophis peronii) is named for the raised, horn-like spines above its eyes, which are unique to this species (2) (3) (4). The rest of the scales on the horned sea snake’s head are irregular and fragmented, with rear borders that are raised and pointed, giving a spiny appearance. This feature becomes more pronounced with age (5) (6).

The horned sea snake is a relatively large sea snake with a small head. Its body is quite slender towards the front, becoming more robust towards the tail (4) (5) (6). The scales of the body are keeled (2) (4) (5), and the scales on the snake’s lips are angular, giving a distinctive zigzagged appearance when viewed from the front (2).

The horned sea snake’s body is usually cream, grey or brown above, with numerous dark cross-bands that taper on the sides (3) (4) (5) (6), and sometimes with small dark bars or spots between the bands (3) (5). The underside of the body is a paler whitish colour (3) (6).

Like other sea snakes, the horned sea snake spends its entire life at sea and is well adapted to its aquatic lifestyle. Its tail is flattened and paddle-like for swimming (2) (4) (7) (8), and its nostrils have valves that allow them to be closed underwater (4) (5) (7). Sea snakes also lack the enlarged belly scales that enable other snakes to move about on land, instead having small scales that allow the body to flatten from side to side, making swimming easier (2) (4).

Although it is widespread around Australia and Southeast Asia, the horned sea snake appears to have separate distributions in the northern and southern hemispheres (1). In the southern hemisphere, it occurs along the northern coast of Australia, from Barrow Island in Western Australia to Moreton Bay in Queensland (5), as well as around southern Papua New Guinea, southern Indonesia, New Caledonia and the Loyalty Islands (1) (5). In the northern hemisphere, the horned sea snake is found from Taiwan south to Thailand, Peninsular Malaysia and Singapore (1).

The horned sea snake is a marine species that typically occurs over sandy substrates on coral reefs (1) (2) (4) (5). This species is found at a range of depths (1).

Like most other sea snakes, the horned sea snake is highly venomous (2) (3) (4), immobilising its prey by injecting venom through the short, fixed, hollow fangs located at the front of its mouth (4) (7). Although the horned sea snake has one of the most toxic venoms of all sea snakes (2) (9), no bites to humans have been documented (2).

The horned sea snake has quite a specialised diet, feeding mainly on gobies (Gobiidae species) and other small fish (2) (4) (5) (8) (10). Younger individuals may also eat shrimps, switching to fish as they get older (2). Usually most active at night (4) (5), the horned sea snake actively hunts for food by searching holes, burrows and crevices for prey (1) (2) (5) (7), which it swallows head first (5).

Like other sea snakes, the horned sea snake is able to avoid accumulating excess salt from its marine environment by excreting it using a specialised gland under the tongue. To rid themselves of encrusting algae and barnacles, sea snakes shed their skin more often than other snakes, about once every two to six weeks (5).

All sea snakes give birth to live young rather than laying eggs (2) (4) (7) (8). The female horned sea snake gives birth to up to ten young at a time, after a gestation period of about six to seven months. This species is thought to give birth every year, with births recorded between March and June in northern Australia. Other aspects of the horned sea snake’s biology, such as its lifespan and the age at which it matures, are currently unknown (5).

The horned sea snake is a widespread species and is not currently considered to be at risk of extinction (1). However, it is often captured as bycatch in trawl fisheries (1) (5), and its slow reproductive rate is likely to make it vulnerable to population declines (5).

The specialised foraging behaviour and diet of this marine reptile also make it vulnerable to disturbances to its coral reef habitat. For example, trawlers may destroy goby burrows in soft bottom habitats, decreasing the amount of prey available to the horned sea snake (1).

Many sea snakes are exploited for their skins, organs and meat, but sea snake fisheries are not always monitored or controlled (8).

In Australia, the horned sea snake is protected under the Environment Protection and Biodiversity Conservation Act 1999, which provides a framework for the protection of Australian species and habitats (1) (5). The Fisheries Management Act 1991 also requires fisheries to avoid capturing protected species such as sea snakes (1). In addition, the horned sea snake occurs in a number of Marine Protected Areas around Australia, including the Great Barrier Reef Marine Park (5).

Conservation efforts underway for the horned sea snake include monitoring levels of bycatch (1). Investigations have shown that certain ‘Bycatch Reduction Devices’ are effective in reducing the number of sea snakes accidentally caught in nets (1) (5) (11), and the routine use of such devices has been recommended (1).